Answer : The correct statement is,
is a reactant; it is present before the reaction occurs.
Explanation :
The given balanced chemical reaction is,
![CaCO_3+2HCl\rightarrow CaCl_2+CO_2+H_2O](https://tex.z-dn.net/?f=CaCO_3%2B2HCl%5Crightarrow%20CaCl_2%2BCO_2%2BH_2O)
Balanced chemical reaction : It is defined as the reaction in which the number of atoms of individual elements present on reactant side must be equal to the product side.
In the chemical reaction, the reactants and products are separated by right arrow.
The species present on the left side of the right arrow is the reactant and the species present on the right side of the right arrow is the product.
In the given balanced reaction,
and
are reactants.
,
and
are products.
Hence, the correct statement is,
is a reactant; it is present before the reaction occurs.